In secondary oil recovery systems, oil is recovered by pumping water into the ground through a secondary hole near the oil deposit. The water seeps through the ground, and as it is under pressure, the water forces the oil to the surface through a primary drill hole. This oil flow, however, will contain oil, water and solid particles. Most of the oil is separated from the rest of the flow at the surface, and the residual liquid is recirculated back into the ground through the secondary drill hole. The use of this residual water substantially reduces the amount of fresh or sea water which must be continually added while the system is in operation.
There is an important drawback to this method. Despite efforts to separate the oil and water at the surface, some oil will be carried back into the ground by the recirculated water. While the oil droplets do not adversely affect the system, other than by possibly confusing detectors trying to detect solid particles in the recirculated flow, the droplets could, if of sufficient quantity or size, put a great deal of oil back into the ground thereby defeating the purpose of the secondary oil recovery system to some degree.